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Cheeseburger blues: could high-fat foods be making us depressed?

New Canadian research points to a conclusion that seems to run counter to what we know: that high-fat 'comfort foods' actually may be making us more depressed.

Fatty "comfort" foods might actually make people depressed, new Canadian research suggests.

Universite de Montreal researchers are reporting that high-fat diets increase anxiety and depressive-like behaviours in mice — a finding that a leading Canadian obesity expert said runs counter to almost everything we have been told about fat-dense foods.

High-fat foods are comforting, said the University of Calgary's Dr. David Lau. Brain scans even show it: they tend to light up different parts of the brain. That suggests fat-rich foods are so "feel good" they could become addictive and explain why obese people tend to gravitate toward them.

But the authors of the new study found the opposite: mice fed highly palatable, high-fat chow displayed behaviours that were more in keeping, in the animal world, with depression and anxiety.

According to lead researcher Dr. Stephanie Fulton, "fat rich foods can actually cause chemical reactions in the brain in a similar way to illicit drugs, ultimately leading to depression as the 'comedowns' take their toll."

Recent studies increasingly suggest that obesity is linked to a higher risk of depression, said Fulton, but exactly why that might be true — what the underlying biological mechanisms are linking the two — remains obscure.

For their study — which appears in the International Journal of Obesity — the researchers studied a strain of mice prone to obesity. One group was fed a diet high in fat, particularly saturated fat, the other low-fat chow.

After 12 weeks, the animals were put through a series of behavioural tests, including "anxiety" tests measuring how rodents respond to a new environment. Stressed animals tend to freeze, or scurry off to a corner, rather than explore.

Mice exposed to the high-fat diet were considerably less active, explored less and avoided open areas.

In a swim test used to measure "behavioural despair" — a test also widely used by drug companies to screen new anti-depressants — mice were forced to swim in a glass cylinder filled with water for six minutes.

"Animals that give up quickly — they stop swimming and just float and stop trying to pull themselves out of the beaker — that's (a sign of) self-helplessness," Fulton said.

Mice on the high-fat diet "actually gave up" and attempted fewer escapes, she said.

When the researchers looked at the animals' brains, they found higher levels of the stress hormone, corticosterone. They also saw changes in the expression of proteins that help control signalling between neurons in areas of the brain regulating emotions and reward.

Fulton said the type of fat might make a difference. Other research has shown that food high in saturated fat — such as hamburgers, bacon, pork sausages, cheese, butter, ice cream — cause inflammation throughout the body, including the brain, and that this inflammation may be causing changes that can lead to "negative mood states." But Fulton's lab has found some evidence that animals consuming the same total amount of fat, but "good fat, like olive oil," experience less anxiety.

The researchers can't rule out the possibility that the extra fat gained by the mice on the high-fat chow affected their performance and "increased immobility times" in the swim test.

They also said it's not clear how to reconcile their results with what others have found. Other teams have reported that rats fed high-fat diets are less anxious and more docile.

But that's only the case in the short-term, Fulton said. Animals, including humans, exposed to a stressful situation — or even long-term, moderate stress — "will have a reduced physiological stress response" — meaning they'll feel a sense of relief — "when given the opportunity to eat high-fat food," said Fulton, a principal investigator at the Centre hospitalier de l'Universite de Montreal and a member of the Montreal Diabetes Research Centre.

"In the short-term high-fat food feels comforting, but in the long-term, and with increasing adiposity (fat mass) it is having negative effects on mood.

"We know that diet is a large contributor to the obesity epidemic throughout the world," Fulton added. Foods high in saturated fats and sugar are particularly abundant, she said.

Lau, editor-in-chief of the Canadian Journal of Diabetes and chair of the diabetes and endocrine research group at U of Calgary, said the story is much more complex.

"We still don't understand why obese people are more depressed — is it related to body image (or other issues)?" he asked.

"Basically what they saw was some association," he said — not cause-and-effect.

It's an interesting hypothesis-generating observation, he said, "but it needs a lot more work. More research is needed, especially in humans, to better understand how nutrient signals affect the hedonic brain pathways."

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